*
* The slice properties dialog in this example is an ordinary GWT modal
* dialog (a DialogBox with modal=True, autoHide=True). It self.gets
* GChart to inform it of click events on the chart by implementing the
* standard GWT ClickHandler interface, and then passing
* itself to GChart's addClickHandler method. The dialog's
* onClick method shows itself (via DialogBox.show)
* and then uses GChart's getTouchedPoint method to self.get a
* reference to the clicked-on slice that it uses to load that slice's
* properties into the form. As the user makes changes via the form,
* they are copied back into the chart and the chart's update
* method is invoked to immediately show the changes on the chart.
*